49 2 CHARLES A. DAVIS 



A partial quantitative analysis of material from the same 

 source, but using stronger acid to affect solution (hydrochloric 

 acid, diluted with four parts of water), gave the following results : 



Insoluble residue - - - - - - -'11.19$ 



Iron and aluminum oxides .... 0.722 



Calcium carbonate ------- 76.00 



Magnesium carbonate ..... 2.359 



Soluble organic matter obtained by difference - - 9.279 



The composition of the insoluble residue was obtained by 

 heating the residue to redness in a platinum crucible for one 

 half hour, and the 11. 19 per cent, of this matter was found to 

 consist of : 



Combustible and volatile matter - 9-243 % = 82.6 % 



Mineral matter - 1-947 = 1 7.4 



The mineral matter was found to be : 



Silica - - - ... . . . 1.787^ = 92.4$ 



Not determined - - - - - .160 = 7.6 



Microscopic examination showed the silica to be largely 

 composed of whole and broken tests of diatoms, minute plants 

 which secrete silicious shells and attach themselves to the Chara 

 stems and branches. 



The mineral matter obtained in this analysis, reduced to parts 

 per hundred, gives the following: 



Per cent. 



Calcium carbonate ..... 93.76 



Magnesium carbonate - 2.93 



Silica and undetermined mineral matter - 2.40 



Iron and aluminum oxides - .89 



This, with a small decrease in the mineral matter and a small 

 amount of organic matter added, would be the composition of 

 ordinary marls, and would be a suitable sample to consider in 

 connection with Portland cement manufacture. 



The large amount of silica may be explained by the fact that 

 the material analyzed was collected at a season when diatoms are 

 especially abundant. 



It may be well to call attention to the fact that in many marls, 

 especially those of large deposits, which the writer has examined 



